High‐Frequency Communications Response to Solar Activity in September 2017 as Observed by Amateur Radio Networks
by Nathan A. Frissell

2019-05-07 147 views

Long before satellite communications, high frequency (HF, 3–30 MHz) radio was the primary method for long distance, over-the-horizon wireless communications. HF signals are able to travel long distances by refracting off of the ionosphere in what is known as “skip” or “skywave” propagation. Aside from a transmitter and receiver, no additional technological infrastructure is needed. Because of this, even in the modern age of space‐borne relays and widely distributed Internet availability, […]

Variable Emission Mechanism of a Type IV Radio Burst
by D. Morosan et al.*

2019-04-23 224 views

Coronal mass ejections (CMEs) are sometimes accompanied by continuum emission at decimetric and metric wavelengths, called Type IV radio bursts. Of particular interest to determining CME properties are moving Type IV radio bursts, which are broadband radio sources moving outwards from the Sun. First studies suggested that moving Type IV bursts are emitted by synchrotron or gyro-synchrotron emitting electrons that are trapped inside CME loops (Dulk 1973). However, since their […]

Remote sensing the coronal magnetic field using solar S-bursts
B. Clarke et al.*

2019-04-09 246 views

Solar activity is often accompanied by solar radio emission. At low frequencies, radio bursts with short durations of <1 s, known as solar S-bursts, have been identified. These intriguing, low frequency bursts were first identified by McConnell (1982) who named them solar S-bursts, owing to their similarity to Jovian S-bursts: the S stands for short or storm. S-bursts appear as narrow tracks on a dynamic spectrum that usually drift from […]

Short-period Waves in Flare Loops: Possible Vehicle for Flare Energy Transport
by Sijie Yu et al

2019-03-26 275 views

Solar flares involve the sudden release of magnetic energy in the solar corona. Accelerated nonthermal electrons have been often invoked as the primary means for transporting the bulk of the released energy to the lower solar atmosphere. However, significant challenges remain for this scenario, especially in accounting for the large number of accelerated electrons inferred from observations. Propagating magnetohydrodynamics (MHD) waves, particularly those with subsecond/second-scale periods, have been proposed as […]

Large area solar flare ribbons as the model to explain puzzling millimeter emission
by G.G. Motorina et al.*

2019-03-12 368 views

Solar flares are sudden explosive processes, that convert the energy of the magnetic field into the kinetic energy of electrons and ions. Since the beginning of the century, millimeter observations of solar flares became routinely possible at a few frequencies with limited spatial resolution (see Kaufmann 2012, as a review). One of the most puzzling aspects of the observations at millimeter wavelengths (200-400 GHz) is the presence, in some flares, […]

Source Imaging of a Moving Type-IV Solar Radio Burst and its Role in Tracking Coronal Mass Ejection From the Inner to the Outer Corona
by Y. Chen et al.

2019-02-26 297 views

T-IV solar radio bursts are wideband continuum observed with dynamic spectrographs at metric to decametric wavelengths. They can be classified into static and moving ones, according to whether the sources remain basically static or move outward. The static ones are related to solar flares with frequencies extending up to GHz, while the moving ones (T-IVms) are related to coronal mass ejections (CMEs) with frequencies sometimes shifting to tens of MHz. […]

Temperature constraints from inversions of synthetic solar optical, UV and radio spectra
by J. M. da Silva Santos et al*

2019-02-12 306 views

While the solar chromosphere has been routinely observed in high-resolution from ground-based optical telescopes such as the Swedish Solar Telescope (SST), and more recently in the UV from space-borne telescopes such as the Interface Region Imaging Spectrograph (IRIS), radio observations lag behind despite their great potential. Distinctly from photospheric lines, most chromospheric diagnostics such as Ca II 854.2 nm and Mg II h and k form under non-LTE conditions, therefore […]

Coronal Mass Ejection-driven Type II solar radio burst structure with LOFAR and radio-wave scattering
by Nicolina Chrysaphi et al.*

2019-01-29 507 views

Coronal Mass Ejections (CMEs) are often viewed as the major drivers of space weather disturbances in the Sun-Earth system. Shocks driven by CMEs can excite radio emissions characterised by a slow frequency drift across dynamic spectra. These radio emissions are known as Type II solar radio bursts and can consist of two bands with a frequency ratio of 1:2. Each of these bands can split into two thinner sub-bands, a […]

1 2 3 14